The present invention relates generally to article manipulation, and particularly to manipulation of entire layers of items during palletizing and de-palletizing operations.
A pallet is a standard support and carrier structure used in shipping. Pallets provide a support surface receiving items stacked for transport. Pallets include a space below the support surface receiving, for example, the tines of a forklift whereby the forklift lifts and moves the pallet with a stack of items thereon. Typically, items are boxes organized in layers upon the pallet. Efficient shipping of palletized items calls for efficient stacking of items on the pallet to minimize open space within the stack. Furthermore, by varying the orientation and/or pattern of items from layer to layer, a stable stack of items may be constructed upon a pallet. Accordingly, a variety of "box patterns" have emerged for efficient and stable packing together of items in item layers on a pallet. The standard pallet is used widely throughout the shipping industry and a variety of apparatus have evolved in relation to the standard pallet for stacking items upon pallets, i.e., palletizing, and for taking items from pallets, i.e., de-palletizing. Thus, palletizing, as used herein, refers to a process constructing a stack of items organized as layers on a pallet. De-palletizing, as used herein, refers to a process breaking-down or removing items from a stack of items on a pallet. Furthermore, the terms palletizing and de-palletizing as used herein shall not be limited to stacking and unstacking relative to a pallet, but shall include generally any stacking or unstacking process relative to articles organized as stacked layers.
A common arrangement for palletizing uses an "apron" to lift from below a layer of items. Once positioned below a layer of items, i.e., by sliding the apron between the layer and a supporting surface therebelow, the apron moves and places the item layer elsewhere. For example, to palletize, the apron moves the layer over a pallet or the top layer of a stack of layers on a pallet. The palletizing device then blocks the layer against movement while the apron slides out from underneath the layer. In this manner, the apron places an entire layer of items upon a pallet or upon the top layer of items on a pallet. Generally, an apron performs only palletizing operations because of the difficulty of inserting an apron between layers of an existing stack of items on a pallet.
Some palletizing and de-palletizing systems operate on an item-by-item basis. In other words, the system receives items individually and constructs, in a palletizing mode of operation, each layer item-by-item on the pallet itself. Similarly, in a de-palletizing mode of operation the system removes items individually from the pallet stack. As may be appreciated, such palletizing and de-palletizing systems are expensive and include complex mechanical and associated control arrangements. With such complex mechanical structures and control arrangements comes more opportunity for malfunction. Complex mechanical structures and control arrangements also significantly increase the cost of manufacture and operation.
U.S. Pat. No. 3,782,564 entitled Product Picking Stacker Crane System, filed Sep. 27, 1971 by Harold S. Burt, shows an overhead crane system transferring item layers from one stack to an adjacent stack. The system is a dual actuator system requiring separate vertical movement actuators and horizontal movement actuators operating in coordination.
U.S. Pat. No. 3,836,018 entitle Discrete Article Palletizing and De-Palletizing apparatus, filed Nov. 5, 1973 by George J. Dawson, et al shows a palletizing device including a top-picking engagement mechanism and a dual actuation drive system, i.e., a horizontal actuation system and a separate vertical actuation system. The illustrated apparatus moves item layers between a first station and a second station.
Thus, article manipulation in the context of palletizing and de-palletizing generally requires relatively complex apparatus and associated complex control schemes. Devices using multiple actuators, e.g., gantry systems with x-y positioning of a load, result in relatively complex and expensive apparatus. Because such systems include separate actuation devices operating in different dimensions, e.g., separate devices for movement in an x dimension and a y dimension, such systems can cause abrupt transition in vertical or horizontal movement and thereby risk loss of a load. To avoid such abrupt transition in movement, elaborate coordination and control must be imposed upon the separate actuation devices to accomplish smooth transition in vertical and horizontal movement.
Thus, it would be desirable to provide a palletizing and de-palletizing apparatus having a simplified structural architecture and a simplified control scheme for reduced overall cost and reduced overall complexity with a smooth transition in movement of loads between pick and place sites.